A disk drive system includes one or more magnetic recording disks and control mechanisms for storing data within approximately concentric tracks on the disk. The magnetic recording disk surface includes a number of radially spaced, concentric tracks, where each track is divided into a number of data sectors. A number of embedded servo sectors forming servo wedges may also be written on each disk surface, which facilitates seeking the head and maintaining the head over the centerline of a target track during read and write operations. The disks are rotated at a constant angular velocity, for example, while varying the data rate from an inner diameter edge to an outer diameter edge of the disk to maximize the recording density.
During the disk manufacturing process, the embedded servo information is preformatted into a pattern on the disk. Conventional servo pre-formatting processes may result in preformatted servo pattern information being eccentric relative to the center of the disk. Conventional methods of pre-formatting servo information including magnetic printing and discrete track media (DTM) process. Both processes rely on a press to mechanically align the servo pattern with the center of the disk. The offset of the center of the pattern relative to the center of the disk is referred to as “eccentricity.”
One conventional method of determining the eccentricity of a disk involves the use of an indicator to measure the runout of the outer diameter (OD) of the disk on the spindle of a spindle stand. The disk is tapped until the OD is determined to be well centered. The spin stand is used to measure the runout of the servo pattern by decoding the servo pattern wedge number and track number. This is not a practical method of determining eccentricity in a manufacturing environment because of the excess time in the factory that would be required to mechanically center every disk that is desired to be measured in a monitoring process.